Booster shots of the Pfizer-BioNTech and Moderna vaccines aren’t just preventing infections with the highly contagious Omicron variant — they’re also keeping infected Americans from ending up in the hospital, according to data published on Friday by the Centers for Disease Control and Prevention.

The extra doses were most effective against infection and death among Americans aged 50 and older, the data showed.

Data from Israel and other countries have also suggested that boosters can help prevent severe illness and hospitalization, especially in older adults.

published additional data showing that in December, unvaccinated Americans 50 years and older were about 45 times more likely to be hospitalized than those who were vaccinated and got a third shot.

Yet less than 40 percent of fully vaccinated Americans who are eligible for a booster shot have received one.

When debating booster shot recommendations for all American adults, scientific advisers to the Food and Drug Administration and the C.D.C.

repeatedly bemoaned the lack of booster shot data that was specific to the United States.

Some members of the Biden administration supported the use of booster doses even before the scientific advisers of the agencies had a chance to review the data from Israel.

now recommends booster shots for everyone 12 years and older, five months after getting two doses of the mRNA vaccines made by Pfizer-BioNtech and Moderna, or two months after a single dose of the Johnson & Johnson vaccine.

Several experts argued at the time that third shots were unnecessary for younger adults because two doses of the vaccine were holding up well.

It was clear even months ago that older adults and those with weakened immune systems would benefit from extra doses of the vaccine, said Dr.